implode vs cave in

implode is not a noun while cave in is a noun.

Word	Noun	Adjective	Verb	Adverb
implode	No	No	Yes	No
cave in	Yes	No	Yes	No

As verbs, cave in is a hypernym of implode; that is, cave in is a word with a broader meaning than implode:

Other hypernyms of implode include break, collapse, fall in, founder, give, give way.

implode (noun)	cave in (noun)
	the sudden collapse of something into a hollow beneath it

implode (verb)	cave in (verb)
burst inward	break down, literally or metaphorically